1. Field of the Invention
The present invention relates to a correcting coil of a deflection yoke for use in a cathode ray tube.
2. Description of the Prior Art
A cathode ray tube which is called a Braun tube of a television receiver includes a deflection yoke mounted on the external periphery of the cathode ray tube at the boundary between a neck and a funnel of the tube for deflecting vertically and horizontally an electron beam emitted from an electron gun contained in the neck located behind the Braun tube to correctly transfer a picture image everywhere on a screen.
Referring to FIG. 1, there is illustrated prior practice of such a deflection yoke for use in a cathode ray tube.
A typical deflection yoke 10 comprises a horn-shaped resin bobbin 1, a horizontal deflection coil (not shown) wound inside the bobbin 1 in a saddle shape, and a vertical deflection coil 2 wound outside the bobbin 1 in a saddle or toroid shape.
Such prior art television receivers, particularly color televisions, have a problem that any picture image is difficult to be seen because of its peripheral edges and the like being displaced. This is caused by a fact that three colors of the picture image are incorrectly superimposed. For solving the problem, a convergence characteristic of such a television receiver must be adjusted by deflecting the electron beams from electron guns such that three electron beams are converged at a single point on a screen even when those beams are deflected toward any location on the screen.
Some measures were taken as methods to adjust the convergence characteristic, such as those of adjusting winding distributions of horizontal and vertical deflection coils of a deflection yoke, and of sticking an image correction member such as a ferrite sheet to an inner surface of a tapered portion of the deflection yoke. For further improving the convergence characteristic, particularly the sensitivity of a green gun, there were mounted on the neck portion 3 of a deflection yoke two or four correcting coils 11 symmetrically arranged about an axial line Z--Z of the cathode ray tube.
Referring to FIG. 2, there is illustrated the prior art correcting coil 11 in the state where it is mounted on the neck portion 3 of the bobbin 1 of the deflection yoke 10.
The correcting coil 11 includes a hollow resin bobbin 13 around which a coil 12 is wound, and a U-shaped core 14 formed by the superimposed or overlapping ends of two L-shaped core members which overlap inside of bobbin 13 for guiding magnetic lines of force. The L-shaped core member comprises superimposed thin silicon steel magnetic pieces 15, 15 of about 0.5 mm thickness for example. The other ends of the L-shaped core members, i.e., tip ends 14a of two legs of the L-shaped core 14, make close contact with the neck portion 3 of the horn-shaped bobbin 1 of the deflection yoke 10 to smoothly guide the magnetic lines of force generated by the correcting coil 11 to the cathode ray.
For increasing the efficiency of the correcting coil 11, i.e., the amount of correction of the magnetic force lines, the following methods are considered:
(1) altering the number of windings of the correcting coil 11, PA1 (2) altering the number or the shape of the cores 14 for use in the correcting coil 11, and PA1 (3) improving close contact conditions between the tip ends 14a of the two legs of the core 14 of the correcting coil 11 and the neck portion 3 of the horn-shaped bobbin 1 of the deflection yoke 10.
These methods however suffer from some difficulties: the method (1) has a problem on the structure and a problem of a sensitivity change (resistance change), the method has an additional problem of a molded member for holding the correcting coil being in need of alteration, and the method (3) has a problem of clearance which might be caused by machining accuracy and a temperature change of the deflection yoke.